The goal of vegetable breeding is to combine various desirable traits in a single variety/hybrid. Such desirable traits may include greater yield, resistance to insects or pests, tolerance to heat and drought, better agronomic quality, higher nutritional value, growth rate and fruit properties.
Breeding techniques take advantage of a plant's method of pollination. There are two general methods of pollination: a plant self-pollinates if pollen from one flower is transferred to the same or another flower of the same plant or plant variety. A plant cross-pollinates if pollen comes to it from a flower of a different plant variety.
Plants that have been self-pollinated and selected for type over many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny, a homozygous plant. A cross between two such homozygous plants of different varieties produces a uniform population of hybrid plants that are heterozygous for many gene loci. Conversely, a cross of two plants each heterozygous at a number of loci produces a population of hybrid plants that differ genetically and are not uniform. The resulting non-uniformity makes performance unpredictable.
The development of uniform lines requires the development of homozygous inbred plants, the crossing of these inbred plants, and the evaluation of the crosses. Pedigree breeding and recurrent selection are examples of breeding methods that have been used to develop inbred plants from breeding populations. Those breeding methods combine the genetic backgrounds from two or more plants or various other broad-based sources into breeding pools from which new lines are developed by selfing and selection of desired phenotypes. The new lines are evaluated to determine which of those have commercial potential.
One crop which has been subject to such breeding programs and is of particular value is the sweet pepper. As used herein, sweet pepper refers to the fruit and the plant of the non-pungent sweet pepper varieties. Sweet peppers belong to the genre Capsicum, of the nightshade family, Solanaceae. The term “sweet pepper” therefore includes bell peppers (Capsicum annuum), the “Thai sweet”—also a cultivar of C. annuum, the “dulce”—a popular cultivar of Capsicum baccatum, as well as Numex Suave Orange (Capsicum chinense), an unusually sweet habanero-type pepper.
Sweet peppers are primarily used as vegetables in cuisine around the world; however, they are also grown for ornamental and medicinal uses. The sweet pepper fruit is eaten cooked or raw. In contrast to the hot pepper, the sweet pepper contains little, if any, capsaicin (8-methyl-N-vanillyl-6-nonenamide), the main active ingredient responsible for the pungency of hot peppers.
C. annuum is a herbaceous annual. The plant has a densely branched stem and grows to 1.5 to 5 feet in height. The fruit is green when unripe, then usually changing to red or brown. The species can grow in many climates; however, they thrive in warm and dry climates.
Most sweet pepper breeding programs have concentrated on the non-pungent varieties of C. annuum, especially bell peppers. Pickersgill and Barbara (1997). Breeding pepper lines with differently colored fruit has been very popular. The color of the fruit can be green, red, yellow, orange and, more rarely, white, purple and brown, depending both on the cultivar and the time of harvest.
Peppers with multiple resistances to several pests and diseases have also been bred. Id. Pickersgill and Barbara (1997). In the case of bell peppers, the development of molecular markers and a molecular linkage map for C. annuum has eased some of the problems associated with selecting simultaneously for multiple resistances and other desirable characteristics. Id. Pickersgill and Barbara (1997). Other sweet pepper breeding efforts have often focused on creating non-pungent cultivars of hot peppers. See e.g. U.S. Pat. No. 7,087,819.
Tetraploidy and haploidy are relatively easy to induce in Capsicum species. In fact, an octaploid Capsicum annuum was recently reported (Pandal et al., 1984). Capsicum species exhibit barriers to interspecific gene transfer. These include unilateral incompatibility, post-fertilization abortion, and nucleo-cytoplasmic interactions leading to male sterility or other abnormalities (Pickersgill and Barbara, 1997). The development of a pepper line resistant to the anthracnose fungal pathogen using interspecific crossing between Capsicum baccatum and C. annuum has been reported (Chae et al., 2003).
Hybrid vigor has also been documented in peppers, and hybrids are gaining increasing popularity among farmers throughout the world, especially in countries with plentiful labor (Berke, 1999).
While breeding efforts to date have provided a number of useful sweet pepper lines with beneficial traits, there remains a great need in the art for new lines with further improved traits. Such plants would benefit farmers and consumers alike by improving crop yields and/or quality.